1. Field of the Invention
The present invention relates to a light emitting device having light emitting elements or light emitting cells for emitting light of a red-based wavelength, which is suitable for improving a Color Rendering Index (CRI) property.
2. Discussion of the Background
Recently, light emitting elements driven under high voltage and AC power have been developed to be used for general illumination. Such a light emitting element has been disclosed in PCT Patent Publication No. WO 2004/023568(A1), entitled “Light-emitting device having light emitting elements” by Sakai et al.
A conventional light emitting element has a plurality of light emitting diodes (hereinafter, referred to as light emitting cells) on a single substrate, and the plurality of light emitting cells are connected in series and reverse parallel through metal wires, which can be used by directly connecting to high voltage or an AC power source.
However, in order to use the conventional light emitting element for illumination, the light emitting element emits blue-based light and the blue-based light is applied to a wavelength converting substance containing a phosphor to be color converted, or the light emitting element is implemented by mixing lights respectively emitted from red, blue and green light emitting elements.
However, since light emitted from the conventional light emitting element has a low CRI, the natural color of an object cannot be clearly shown when the light is thrown on the object.
FIG. 1 is a graph showing the CRI property when a blue light emitting chip is provided and a wavelength converting substance containing a yellow phosphor is applied to the blue light emitting chip.
Meanwhile, FIG. 2 is a graph showing the CRI property when lights emitted from red, blue and green light emitting elements are mixed.
According to the conventional light emitting element, an intensity of red-based light is extremely weak compared with those of blue- and green-based lights. In this case, it is difficult to express a red-based color, and thus the CRI property essential to a light source for illumination may be lowered.
In particular, the CRI property (color rendering) is considered as being very important in the illumination facility market. Thus, it is required to improve the CRI property in order to use a light emitting diode (LED) as a light source for illumination.